The present invention relates to a method and system for the analysis of oximetry data for the detection of sleep-disordered breathing therefrom. More specifically, the present invention relates to a system that employs an algorithm to reliably detect patient arousals and correlate those with accelerated heart rate and oxygen saturation levels in a manner that detects sleep-disordered breathing via a patient's oximetry data.
Nearly one in seven people in the United States suffer from some type of chronic sleep disorder. Further, only 50% of people are estimated to get the recommended amount of seven to eight hours of sleep each night. Estimates indicate that sleep deprivation and its associated medical and social costs may exceed $150 billion per year. The primary sleep disorders affecting approximately 50 million Americans include narcolepsy, restless legs/periodic leg movement, insomnia, and sleep apnea. Sleep apnea is defined as the cessation of breathing during sleep and is categorized as obstructive sleep apnea (OSA), central sleep apnea (CSA), and complex sleep apnea (CompSA). OSA is characterized by repetitive pauses in breathing during sleep due to the obstruction and/or collapse of the upper airway (throat), usually accompanied by a reduction in blood oxygen saturation, and often followed by an awakening to breathe (an apnea event). Respiratory effort continues during the episodes of OSA. Multiple episodes of apnea may occur in one night, causing sleep disruption. CSA is a neurological condition causing cessation of all respiratory effort during sleep, usually with corresponding decreases in blood oxygen saturation. In contrast to OSA, where there is respiratory effort from the brain stem but a physical blockage prevents inhalation of oxygen, in CSA the brainstem center controlling breathing shuts down, resulting in no respiratory effort and no breathing. The subject is aroused from sleep by an automatic breathing reflex. Frequent activation of the reflex results in very little sleep for the subject. The neurological mechanism behind CSA is very different from the physical cause of OSA. Although the effects of CSA and OSA are highly similar, effective treatment can differ. CompSA can be thought of as a combination of OSA and CSA. As mentioned before, CompSA is characterized by an emergence of CSA events after CPAP initiation.
Apnea treatment is provided based on the type of apnea, and can be adjusted by re-testing the subject at some later time to determine whether the condition or the symptoms have been alleviated. The most common method of treating OSA is continuous positive airway pressure (CPAP) and positive airway pressure (PAP) devices applied to the subject's airway to force the subject to breathe. When using a simple CPAP device to treat OSA, the air pressure acts as a splint, holding the airway open and reducing or removing the obstruction. The optimal pressure is determined by a sleep technician during a single titration night. The sleep technician manually adjusts the device to deliver a minimum pressure sufficient to force the airway open and reduce the number of apneas. Once the optimal pressure is determined, the device is programmed to consistently provide this pressure, and the patient is sent home.
In order to discover the airway pressure which is most effective for a particular individual, the practice has been for the patient to undergo two sleep studies at an observation facility such as a hospital, clinic or laboratory. The first night is spent observing the patient in sleep and recording selected parameters such as oxygen saturation, chest wall and abdominal movement, air flow, expired carbon dioxide, ECG, EEG, EMG and eye movement. This information can be interpreted to diagnose the nature of the sleeping disorder and confirm the presence or absence of apnea and where present the frequency and duration of apneic episodes and extent and duration of associated oxygen desaturation.
The second night is spent with the patient undergoing nasal CPAP therapy. When apnea is observed the CPAP setting is increased to prevent the apnea. The pressure setting at the end of the sleep period, i.e., the maximum used, is deemed to be the appropriate setting for that patient. For a given patient in a given physical condition there will be found different minimum pressures for various stages of sleep in order to prevent occlusions. Furthermore, these various pressures will, in fact, vary from day to day depending upon the patient's physical condition, for example, nasal congestion, general tiredness, effects of drugs such as alcohol, as well as their sleeping posture. Thus the appropriate pressure found in the laboratory is necessarily the maximum of all these minimum pressures for that particular night and is not necessarily the ideal pressure for all occasions nor for every night. It will generally be higher than necessary for most of the night.
As can be seen there exists the inconvenience and cost of diagnosis which is currently undertaken by overnight observation at a sleep clinic or the like. Hence a simple means whereby a patient's apnea problem can be diagnosed at home without supervision is clearly desirable. There is therefore a need for a system that can quickly and reliably identify a patient's apnea condition without having to undertake a full laboratory based sleep study. There is a further need for a system that can be deployed in a home environment and record a patient's vital signs over the course of a sleep cycle in a manner that then allows reliable identification of a patient's apnea condition without having to undertake a full laboratory based sleep study.